Lithographic apparatus and device manufacturing method

ABSTRACT

Embodiments of a drain in a lithographic projection apparatus are described that have, for example, a feature which reduces inflow of gas into the drain during a period when no liquid is present in the drain. In one example, a passive liquid removal mechanism is provided such that the pressure of gas in the drain is equal to the ambient gas pressure and in another embodiment a flap is provided to close off a chamber during times when no liquid needs removing.

FIELD

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus). Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thisrequires additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate using a liquidconfinement system (the substrate generally has a larger surface areathan the final element of the projection system). One way which has beenproposed to arrange for this is disclosed in PCT patent publication WO99/49504, hereby incorporated in its entirety by reference. Asillustrated in FIGS. 2 and 3, liquid is supplied by at least one inletIN onto the substrate, preferably along the direction of movement of thesubstrate relative to the final element, and is removed by at least oneoutlet OUT after having passed under the projection system. That is, asthe substrate is scanned beneath the element in a −X direction, liquidis supplied at the +X side of the element and taken up at the −X side.FIG. 2 shows the arrangement schematically in which liquid is suppliedvia inlet IN and is taken up on the other side of the element by outletOUT which is connected to a low pressure source. In the illustration ofFIG. 2 the liquid is supplied along the direction of movement of thesubstrate relative to the final element, though this does not need to bethe case. Various orientations and numbers of in- and out-letspositioned around the final element are possible, one example isillustrated in FIG. 3 in which four sets of an inlet with an outlet oneither side are provided in a regular pattern around the final element.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

In European patent application publication no. EP 1420300 and UnitedStates patent application publication no. US 2004-0136494, each herebyincorporated in their entirety by reference, the idea of a twin or dualstage immersion lithography apparatus is disclosed. Such an apparatus isprovided with two tables for supporting a substrate. Levelingmeasurements are carried out with a table at a first position, withoutimmersion liquid, and exposure is carried out with a table at a secondposition, where immersion liquid is present. Alternatively, theapparatus has only one table.

Handling immersion liquid in a lithographic apparatus brings with it oneor more problems of liquid handling. A gap normally exists between anobject, such as a substrate and/or a sensor, and a substrate tablearound the edge of the object (e.g., substrate). U.S. patent applicationpublication US 2005-0264778, herein incorporated in its entirety byreference, discloses filling that gap with material or providing aliquid source or low pressure source to deliberately fill the gap withliquid in order to avoid bubble inclusion as the gap passes under theliquid supply system and/or to remove any liquid which does enter thegap.

SUMMARY

It is desirable, for example, to provide for removal of liquid from agap between an edge of an object and a substrate table on which theobject is positioned. The object may be a substrate, a sensor, a closingplate, etc.

According to an aspect of the invention, there is provided alithographic apparatus, comprising a substrate table constructed to holda substrate; a liquid supply system configured to provide a liquid to aspace between an object on the substrate table and a projection system;and a drain in the substrate table configured to contain liquid whichleaks, in use, between an edge of the object and the substrate table,wherein, in use, pressure of gas in the drain is maintained to besubstantially equal to ambient pressure of gas above the substratetable.

According to an aspect of the invention, there is provided alithographic apparatus, comprising a substrate table constructed to holda substrate; a liquid supply system configured to provide a liquid to aspace between an object on the substrate table and a projection system;and a chamber in the substrate table in fluid communication with a gapsurrounding, in use, an outer edge of the object such that the chamberis open to an outer surface of the substrate table at a position aroundthe outer edge of the object, wherein, in use, the liquid has a contactangle of greater than 45° with surfaces which define the gap and faceeach other across the gap.

According to an aspect of the invention, there is provided alithographic apparatus, comprising a substrate table constructed to holda substrate; a liquid supply system configured to provide a liquid to aspace between an object on the substrate table and a projection system;and a chamber in the substrate table in fluid communication with a gapsurrounding, in use, an outer edge of the object such that the chamberis open to an outer surface of the substrate table at a position aroundthe outer edge of the object, wherein, in use, the angle betweensurfaces defining the gap and surfaces of the chamber onto which the gapopen is at least 90°.

According to an aspect of the invention, there is provided alithographic apparatus, comprising a substrate table constructed to holda substrate, the substrate table comprising a passage which leads to achamber, the passage connecting the chamber to an outer surface of thesubstrate table and, in use, surrounds an outer edge of an object on thesubstrate table; and a flexible flap extendable across the passage andbiased substantially to block flow of gas between the passage and thechamber and deformable by hydrostatic and/or hydrodynamic pressure fromabove to unblock the gap to allow passage of liquid from the passageinto the chamber.

According to an aspect of the invention, there is provided alithographic apparatus, comprising a liquid supply system configured toprovide a liquid to a space between a projection system and a substrate;a first substrate table configured to hold a substrate, the firstsubstrate table having an edge with a face with a vertical component;and a second substrate table configured to hold a substrate, the secondsubstrate table having an edge with a face with a vertical component,wherein, in use, the liquid has a contact angle of greater than 45° withat least a portion of at least one of the faces.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting a patterned beam of radiationthrough a liquid onto a substrate and collecting liquid which leaksbetween an edge of an object and a substrate table configured to holdthe substrate in a drain which is maintained at ambient pressure.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting a patterned beam of radiationthrough a liquid onto a substrate and collecting liquid in a chamber viaa gap between an object and a substrate table configured to hold thesubstrate, the liquid having a contact angle of greater than 45° withsurfaces which define the gap and face each other across the gap.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting a patterned beam of radiationthrough a liquid onto a substrate wherein liquid which leaks between anobject on a substrate table configured to hold the substrate, travelsalong a passage and moves a flexible flap extending across an outlet ofthe passage to expose the liquid to a low pressure such that it isremoved from the flexible flap to allow the flexible flap to re-blockthe passage.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting a patterned beam of radiationwith a projection system through a liquid onto a substrate which issupported by a first substrate table, positioning a second substratetable next to the first substrate table and moving both substrate tablestogether under the projection system such that the second substratetable is moved under the projection system, wherein edges of the firstand second substrate tables which are positioned next to each otherduring the moving each comprise a face with a vertical component,wherein the liquid has a contact angle of greater than 45° with at leasta portion of at least one of the faces.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts a localized area liquid supply system;

FIG. 6 illustrates, in cross-section, a drain in a substrate tableaccording to an embodiment of the invention;

FIG. 7 illustrates, in cross-section, a drain in a substrate tableaccording to an embodiment of the invention;

FIGS. 8 a to 8 e illustrate, in cross-section, variations of a drain ina substrate table according to an embodiment of the invention; and

FIGS. 9 a and 9 b illustrate, in cross-section, a drain according to anembodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

an illumination system (illuminator) IL configured to condition aradiation beam B (e.g. UV radiation or DUV radiation);

a support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positionerPM configured to accurately position the patterning device in accordancewith certain parameters;

a substrate table (e.g. a wafer table) WT constructed to hold asubstrate (e.g. a resist-coated wafer) W and connected to a secondpositioner PW configured to accurately position the substrate inaccordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PSconfigured to project a pattern imparted to the radiation beam B bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure holds the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, vacuum, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more support structures). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Although the present invention can be used with any type of liquidsupply system, the design is optimized for use with a localized arealiquid supply system such as that illustrated in FIG. 5. In this type ofliquid supply system, liquid is only provided to a small area of thetotal top surface of a substrate at any one time. It is illustrativebriefly to describe the operation of a localized area liquid supplysystem.

Referring to FIG. 5, the localized area liquid supply system comprises aliquid supply system with a liquid confinement structure which extendsalong at least a part of a boundary of the space between the finalelement of the projection system and the substrate table. The liquidconfinement structure is substantially stationary relative to theprojection system in the XY plane though there may be some relativemovement in the Z direction (in the direction of the optical axis). Inan embodiment, a seal is formed between the liquid confinement structureand the surface of the substrate and may be a contactless seal such as agas seal.

The liquid confinement structure 12 at least partly contains liquid inthe space 11 between a final element of the projection system PL and thesubstrate W. A contactless seal 16 to the substrate may be formed aroundthe image field of the projection system so that liquid is confinedwithin the space between the substrate surface and the final element ofthe projection system. The space is at least partly formed by the liquidconfinement structure 12 positioned below and surrounding the finalelement of the projection system PL. Liquid is brought into the spacebelow the projection system and within the liquid confinement structure12 by liquid inlet 13 and may be removed by liquid outlet 13. The liquidconfinement structure 12 may extend a little above the final element ofthe projection system and the liquid level rises above the final elementso that a buffer of liquid is provided. The liquid confinement structure12 has an inner periphery that at the upper end, in an embodiment,closely conforms to the shape of the projection system or the finalelement thereof and may, e.g., be round. At the bottom, the innerperiphery closely conforms to the shape of the image field, e.g.,rectangular though this need not be the case.

The liquid is contained in the space 11 by a gas seal 16 which, duringuse, is formed between the bottom of the liquid confinement structure 12and the surface of the substrate W. The gas seal is formed by gas, e.g.air or synthetic air but, in an embodiment, N₂ or another inert gas,provided under pressure via inlet 15 to the gap between liquidconfinement structure 12 and substrate and extracted via outlet 14. Theoverpressure on the gas inlet 15, vacuum level on the outlet 14 andgeometry of the gap are arranged so that there is a high-velocity gasflow inwards that confines the liquid. Those inlets/outlets may beannular grooves which surround the space 11 and the flow of gas 16 iseffective to contain the liquid in the space 11. Such a system isdisclosed in United States patent application publication No. US2004-0207824, hereby incorporated in its entirety by reference.

Other solutions are possible and one or more embodiments of the presentinvention are equally applicable to those. For example, in place of thegas seal 16 it is possible to have a single phase extractor which onlyextracts liquid. Radially outwardly of such a single phase extractorcould be one or more features to produce a gas flow to help contain theliquid in the space. One such type of feature might be a so-called gasknife in which a thin jet of gas is directed downwards onto thesubstrate W. During scanning motion of the substrate under theprojection system and the liquid supply system, hydrostatic andhydrodynamic forces may be generated which result in pressures on theliquid downwards towards the substrate.

With a localized area liquid supply system the substrate W is movedunder the projection system PL and the liquid supply system and when anedge of the substrate W is to be imaged or when a sensor on thesubstrate table is to be imaged or the substrate table is to be movedsuch that a dummy substrate or so-called closing plate can be positionedunder the liquid supply system to enable substrate swap to take place,an edge of the substrate W will pass under the space 11 and liquid mayleak into the gap between the substrate W and substrate table WT. Thisliquid may be forced in under hydrostatic or hydrodynamic pressure orthe force of a gas knife or other gas flow creating device.

Although one or more embodiments of the invention will be describedbelow in relation to providing a drain around the edge of a substrate W,one or more embodiments are equally applicable to one or more otherobjects placed on the substrate table including, but no limited to, aclosing plate used to maintain liquid in the liquid supply system bybeing attached to the bottom of the liquid supply system during, forexample, substrate swap and/or one or more sensors. Thus, any referencebelow to the substrate W should be considered to be synonymous with anyother object, such as a sensor or closing plate.

FIG. 6 illustrates an embodiment of the present invention. FIG. 6 is across-section through a substrate table WT and a substrate W. A drain 10is provided around the outer edge of the substrate W where a gap 15between the substrate W and the substrate table WT exists. In anembodiment, the drain 10 extends around the periphery of the substrateW. In an embodiment, the drain 10 may only extend around part of aperiphery of the substrate W.

A substrate W is held on substrate table WT during imaging of thesubstrate W. The substrate W is positioned on a pimple table 20 which isa chuck with a plurality of projections 22. An under pressure generatedin the gap between the substrate W and the surface of the substratetable WT between the projections 22 clamps the substrate W onto theprojections 22.

In order to account for tolerances in the exact size of the substrate Wand the fact that a substrate W may not be positioned perfectlycentrally on the pimple table 20, the substrate table WT is constructedand arranged such that a gap/groove/passage 15 is provided between thesubstrate W and a top portion of the substrate table WT to account forthe tolerances.

The top portion of the substrate table WT is constructed and arrangedsuch that its top surface will be substantially parallel and co-planarwith the top surface of the substrate W when the substrate W is placedon the substrate table WT. This is to ensure that when an edge of thesubstrate W is being imaged or when the substrate table WT passes underthe projection system to bring the substrate W under the projectionsystem for the first time or to move the substrate W out from under theprojection system following imaging, and the liquid supply system mustpass from the top surface of the substrate table WT to the top surfaceof the substrate W or vice versa, leaking of liquid into gap 15 will bereduced or minimized. However, some liquid will inevitably enter the gap15.

In an embodiment, the gap 15 is provided with a low pressure source inorder to remove liquid which enters the gap 15. However, the lowpressure source may create a flow of gas across the edge of thesubstrate W when the edge of the substrate W is not being imaged and istherefore not covered in liquid. This flow of gas may cause localizedcooling of the substrate W which is deleterious.

In an embodiment, no liquid removal device may be provided to removeliquid from the gap 15 (for example, the gap may be blocked with apliant material). Although this overcomes the problem of localizedcooling of the substrate W, unfortunately this may lead to the inclusionof bubbles in the liquid in the liquid supply system (as the gap passesunder the liquid supply system) thereby possibly introducing imagingerrors. Furthermore or alternatively, contact between a (solid) sealmember and the substrate W is desirably avoided as there is a danger ofsubstrate damage and/or particle generation.

One or more embodiments are directed to alleviating one or more of theseproblems or other problems. One or more embodiments have an advantage ofreducing the amount of liquid lost from the liquid supply system throughthe gap 15.

The construction of the drain 10 will now be described in detail withreference to FIG. 6. In FIG. 6 the gap or passage or groove 15 has twodistinct vertical elements. The top element of the gap is definedbetween the substrate W and the top portion of the substrate table WT.The narrowest part of the gap 15 which is the lower element is definedbetween two projections 40, 60 of the substrate table WT. The radiallyinward projection 40 extends radially outwardly from or under the pimpletable 20 such that its edge is substantially vertically aligned with theedge of the substrate W. However, the edge of the projection 40 mayeither be radially inwardly or radially outwardly of the substrate W.The outer projection 60 projects radially inwardly further inwards thanthe top portion of the substrate table WT but again this is notnecessarily the case and it could project less. Indeed, the outerprojection 60 could be missing and the top portion of the substratetable WT could extend downwards to form the projection. Thus, each sideof the gap 15 is defined by one projection of the substrate table WT.

The gap or passage or groove 15 brings a chamber 70 into fluidcommunication with the atmosphere above the substrate table WT. In anembodiment, a line can be drawn straight from outside of the substratetable WT through the gap 15 between projections 40, 60 into the chamber70. In an embodiment, that line is a vertical line and/or intercepts theboundary of the chamber 70 on the bottom wall 72 of the chamber 70. Ifthe dimensions of the gap 15 and chamber 70 are correctly chosen thisarrangement has an advantage of meaning that a gas knife which may beused in the liquid supply system in order to help contain liquid withinthe space is not influenced by the presence of the gap 15, because thegas knife does not “feel” the bottom of the chamber 70. In order forthis effect (or more precisely lack of effect) to be present, the bottom72 of the chamber 70 should be at least 1 mm, at least 2 mm, at least 3mm, at least 4 mm or at least 5 mm from the top surface of the substratetable WT.

In the drain of FIG. 6, the pressure of gas in the chamber 70 ismaintained at the same pressure as gas outside of the substrate table WT(i.e. ambient gas pressure). This means that there is, in normaloperation, substantially no gas flow through the gap 15 when the gap 15is not covered by the liquid supply system and one or more gas flowdevices of the liquid supply system are blowing gas through the gap 15.Even if the liquid supply system covers part of the gap 15 (the gap 15surrounding the periphery of the substrate W and the liquid supplysystem providing liquid to a space which is far smaller than the topsurface area of the substrate W) ambient pressure will still bemaintained in the chamber 70 because the chamber 70 is annular (or othershape) and will be open to the atmosphere above the substrate table WTthrough the gap 15 at another location around the periphery of thesubstrate W.

In order to remove liquid from the chamber 70, a liquid removal deviceis employed which does not create an underpressure in the chamber 70. Inan embodiment, the liquid removal device does not substantially create agas flow in the chamber 70. For example, the liquid removal device couldbe a passive liquid removal device using, for example, capillary actionin a capillary passage 80 for the removal of liquid. If the immersionliquid has a contact angle of less than 90°, or less than 80°, 70°, 60°,50°, 40°, 30°, or 20° with the inner surface of the capillary passage80, removal of liquid sitting on the bottom 72 of the chamber 70 shouldbe greatly enhanced. One or more other liquid removal devices may beusable, for example one which only applies an under pressure to passage80 when the presence of liquid at the mouth of the passage 80 in thechamber 70 is detected or a microsieve single phase extractor (seeEuropean patent application publication EP 1,628,163 for example). Inanother way, one part of an embodiment of the invention may be seen asnot using active suction to remove liquid from the gap 15 (and chamber70), particularly when no liquid is present.

In use, it is possible to make the gap 15 small enough such that surfacetension of the immersion liquid means that the immersion liquid willbridge the gap between the substrate W and the substrate table WT whenthe gap 15 traverses the edge of the barrier member of the liquid supplysystem. However, hydrostatic and/or hydrodynamic pressures in use and/orpressures due to scanning movement may mean that the surface tension ofthe liquid is not enough to prevent liquid from entering the gap 15 andpassing between projections 40, 60 into chamber 70. However, because theliquid is removed from the chamber 70 in a passive manner withoutcreating an under pressure in the chamber 70, single phase extraction ofliquid from the gap into the chamber 70 is possible such that bubblesare unlikely to be introduced into the liquid in the space. In otherwords, liquid will simply flow into the gap 15 and fill the gap beforedripping into the chamber 70 and any gas in the gap 15 will be eitherforced into the chamber 70 or forced out sideways along the gap 15.

Because no under pressure is applied to the chamber 70 the rate ofliquid loss through the groove or passage or gap 15 should be vastlyreduced over the case when an under pressure is applied to the chamber70.

In order to reduce the flow of liquid through the gap 15, the surfaceproperties of the faces defining the gap and facing each other (whichare labelled 42, 62) may be specifically configured. For example, if theimmersion liquid (e.g. ultra pure water (UPW)) has a contact angle ofgreater than 45° with the surfaces of those faces 42, 62 under theoperating conditions in the lithographic apparatus e.g. of intense UVradiation and UPW flow (i.e. those faces are mildly hydrophobic underthe operating conditions) the strength of any meniscus of liquidextending between those two surfaces will often be high enough toovercome the hydrostatic and hydrodynamic forces of the liquid above themeniscus. In an embodiment, the immersion liquid has a contact angle ofgreater than 70°, 80°, or 90° with the surfaces which define the gap andface each other across the gap. In an embodiment, the faces 42, 62define the narrowest part of the gap 15.

The strength of the meniscus may also be increased by changing thegeometry of the faces 42, 62. If the shape of those faces is changed toenhance capillary action the need to ensure that the immersion liquidhas a contact angle of greater than 45° with the surfaces of those facesmay be reduced. As is illustrated in dotted lines in FIG. 6, if thelower edges of the gap 15 are provided as sharp edges (e.g. the walls ofthe gap meet the walls of the chamber at an angle of greater than 90°,greater than 100° or greater than 110°) a capillary lock may be formed.Some other solutions to reduce liquid loss are illustrated in FIG. 8.

Some liquid may leak through in certain circumstances, for example whenthe gap 15 passes under the edge of the barrier member liquid will beleft in the gap 15. The gap 15 may then pass under a gas knife which maybe part of the liquid supply system blowing on top of the liquid in thegap and causing it to drop into the chamber 70. Actually this processmay be beneficial because it means that the gap is completely clearedsuch that the next time the gap 15 at that point along the gap passesunder the space 11 of immersion liquid the liquid may fill the gap 15with a reduced danger of gas in the gap finding its way as bubbles intothe immersion liquid in the space (because any gas can escape and is notconfined by liquid droplets in the gap). The hydrostatic and scanningpressures induced in the immersion liquid may ensure the proper flowdirection of liquid through the gap 15 avoiding bubbles to form and riseinto the space. Also, the liquid may be cleared from the gap by the gasknife without flowing back onto the substrate and substrate table.Splashing and associated defects may be avoided in this way.

As illustrated in FIG. 6, the projections 40, 60 defining the gap 15 areillustrated with convex faces 42, 62 facing each other. Thus, theprojections 40, 60 define the narrowest portion of the gap 15 at a midportion or point between those two projections. Other shapes may bepossible including, but not limited to the shape illustrated in FIG. 8.

One or more embodiments of invention may also be applicable to the wayin which a gap between two substrate tables WT may be bridged duringsubstrate swap without the use of a closing plate. In this method twosubstrate tables are moved close together and then moved together underthe projection system such that the liquid supply system “moves” fromone substrate table to the other. In this case the edge of the substrateW illustrated in FIG. 6 is replaced by the edge of a first substratetable WT1 such that this first substrate table WT1 provides theprojection 40 on the left hand side of FIG. 6 and a second substratetable WT2 provides the protrusion 60 on the right hand side of FIG. 6.In an embodiment, some sort of drain would be attached to one or otheror both of the substrate tables WT1, WT2 but because the drain (which isreplacing the chamber 70) is at atmospheric pressure, this does notpresent a problem.

In an embodiment, the dimensions of the chamber 70 are that it should beat least twice as wide as the gap 15 in order to ensure that any liquidwhich does enter the gap 15 does not travel too far past the substrate Wwithout first breaking up. Arranging for the transition of the width ofthe gap 15 to the width of the chamber 70 to be large and sudden ensuresthat the liquid meniscus which bridges between the projections 40, 60 isdesirably broken at that point such that liquid will flow into thechamber 70 and drip onto the bottom surface 72 where it can be removedby the liquid removal device 80. In an embodiment, tthe chamber orgroove is at least 1 mm wider than the gap 15.

As is illustrated in FIG. 6, the gap 15 is positioned over the center ofthe chamber 70. This is not necessarily the case and the gap 15 may bepositioned any where along the width of the chamber 70 from the extremeleft hand side to the extreme right hand side (the innermost andoutermost sides) as illustrated in FIG. 6.

FIG. 7 illustrates an embodiment of the present invention which is thesame as the embodiment described above with respect to FIG. 6 except asdescribed below. In this embodiment, the narrowest point of the gap 15is defined by the distance between the edge of the substrate W and thetop portion of the substrate table WT. Thus the projections 40, 60 ofthe first embodiment are not present and are replaced by the edge of thesubstrate W and top portion of the substrate table WT respectively(i.e., these form respectively the projections 40, 60). A material usedfor a substrate table WT is normally hydro or liquid-philic meaning thatthe immersion liquid has a contact angle of less than 90° with a surfaceof the substrate table WT. In an embodiment, the edge of the substrate Wmay be made to be hydro or liquid phobic (i.e. the immersion liquid hasa contact angle of greater than 90° with the surface) and the same canbe done for the edge of the substrate table WT which defines the otherside of the gap 15. This is similar to what is described above.

FIG. 8 illustrates an embodiment which is the same as the embodimentdescribed above with respect to FIG. 7 except as described below. Thisembodiment is optimized for low liquid consumption. Because the gap inFIG. 7 cannot be reduced any more (because of substrate dimensionaltolerances) a different projection shape is chosen (FIG. 8 a) so as tominimize the width of the gap 15 while still enabling suitable substratetable tolerances for variations in substrate size.

In the FIG. 8 a embodiment, the convex surface of at least one of thetwo projections is replaced by a concave surface. The concave surface isnearest to the other side of the gap nearest to the chamber 70. In thisway, because of the curvature of the edge of the substrate W itself, thesubstrate W can get closer to the projection thereby narrowing the gap.A shorter meniscus is thereby needed to bridge the gap between thesubstrate W and substrate table WT. A shorter meniscus is stronger thana long one.

FIGS. 8 b-8 e illustrate other measures which may be taken to narrow thegap without unnecessarily impeding the path for the gas of the gas knifeof the liquid confinement structure 12 i.e. the “bottomless” characterof the drain which means that the gas knife does not “feel” the bottomof the chamber 70. In these embodiments at least one divider ispositioned in the chamber 70 under the gap 15 to split the opening ofthe gap into the chamber into two or more gaps.

In the embodiment illustrated in FIG. 8 b, a bar 200 is positioned underthe gap 15, in an embodiment along the entire length of the gap 15 suchthat the bar 200 is an annulus (or other peripheral shape). The bar 200splits the gap 15 into two parts such that two shorter meniscuses wouldbe present, one between the bar and the substrate W or the substratetable WT directly under the substrate W, and one between the bar 200 andthe substrate table WT on the right hand side of the bar 200, asillustrated in FIG. 8 b. However, the bottomless character of the drainis not impeded because gas from a gas knife would easily pass eitherside of the bar 200 into the chamber 70.

The embodiment of FIG. 8 c is similar to that of the embodiment of FIG.8 b except that the bar 200 has been replaced by a series of vanes 210.These vanes or fins 210 are arranged such that they form a plurality ofgaps or passages between each other from the gap 15 into the chamber 70.Thus, the fins 210 may be seen as elongate structures in cross-sectionwhich have a length which, in an embodiment, extends all along thebottom of the gap 15 to form several annuli (or other peripheralshapes). Four fins 210 are illustrated. However, the skilled person willappreciate that any number could be provided. The fins split up thewidth of the gap 15 into several smaller gaps across which the liquidmeniscus needs to bridge.

The embodiment in FIG. 8 d illustrates a further idea in which a mesh220 is placed under the gap 15 such that it bridges the gap between thesubstrate table WT on the left hand side of the gap 15 and the substratetable WT on the right hand side of the gap 15. Again, in an embodiment,it extends all around the gap 15. The grid or gauze or mesh 220 presentsthe liquid with many gaps across which a meniscus must bridge therebyproviding many narrow gaps for the liquid to pass through. However, evensuch a grid or gauze or mesh would not present much resistance to flowof gas through it.

FIG. 8 e shows another embodiment in which the gap is split into two. Inthis case a single plate 230 is placed in the center of the gap therebyto split up the gap into two and reduce the width across which liquidmust bridge. In the embodiment of FIG. 8 e only a single plate isprovided which is given a thickness (in contrast to the embodimentillustrated in FIG. 8 c with a plurality of fins). In the embodiment ofFIG. 8 e the plate 230 is shown as being vertical. However, the plate230 does not necessarily need to be vertical and it could be angled inthe same way as some of the fins 210 in the embodiment of FIG. 8 c.

FIGS. 9 a-b illustrate an embodiment which is the same as the embodimentdescribed above with respect to FIG. 6 except as described below. Inthis embodiment, a flap 100 is provided to seal the entrance of the gap15 to the chamber 70. In FIG. 9 a the gap 15 is illustrated as being atortuous path from the edge of the substrate W into the chamber 70.However, a gap 15 as illustrated in FIG. 6, 7 or 8 may also be employedin this present embodiment.

The flap 100, which is a flexible flap, extends along the entireperiphery of the gap 15. The flap 100 is attached to the substrate tableat either its inner most or outer most edge. In this embodiment anactive liquid removal device is provided such that the chamber 70 isheld at an under pressure in which the pressure is lower than theambient pressure. In order to avoid a flow of gas across the surface ofthe edge of the substrate W when the liquid supply device is notpositioned at that point along the gap 15, the flap is biased such thatit covers the entrance of the gap 15 into the chamber 70. When liquidenters the gap 15, and is forced along the gap 15 onto the flap 100, thematerial properties of the flap and dimensions of the flap 100 arechosen such that the weight and/or hydrodynamic pressure of the liquidon top of the flap will force the flap downwards at the edge at which itis not attached to the substrate table (as is illustrated in FIG. 9 b)so that liquid can flow into the chamber 70 where it is sucked away bythe active liquid removal device. Clearly once all the liquid isremoved, the flap 100 will move back to the position where it isblocking the passage 15 into the chamber 70 due to being biased in thatdirection.

Once the flap has been moved away from sealing the gap as illustrated inFIG. 9 b, the liquid whose weight and/or hydrodynamic pressure forcedthe flap 100 to open will be exposed to the under pressure in thechamber 70 and will be sucked into the chamber 70 and removed from thechamber 70 by the active liquid removal device 180.

Thus, in this embodiment flow of gas over the edge of the substrate mayprevented.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography atopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm) andextreme ultra-violet (EUV) radiation (e.g. having a wavelength in therange of 5-20 nm), as well as particle beams, such as ion beams orelectron beams.

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and electrostaticoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above and whether the immersion liquid is provided in the formof a bath or only on a localized surface area of the substrate. A liquidsupply system as contemplated herein should be broadly construed. Incertain embodiments, it may be a mechanism or combination of structuresthat provides a liquid to a space between the projection system and thesubstrate and/or substrate table. It may comprise a combination of oneor more structures, one or more liquid inlets, one or more gas inlets,one or more gas outlets, and/or one or more liquid outlets that provideliquid to the space. In an embodiment, a surface of the space may be aportion of the substrate and/or substrate table, or a surface of thespace may completely cover a surface of the substrate and/or substratetable, or the space may envelop the substrate and/or substrate table.The liquid supply system may optionally further include one or moreelements to control the position, quantity, quality, shape, flow rate orany other features of the liquid.

The immersion liquid used in the apparatus may have differentcompositions, according to the desired properties and the wavelength ofexposure radiation used. For an exposure wavelength of 193 nm, ultrapure water or water-based compositions may be used and for this reasonthe immersion liquid is sometimes referred to as water and water-relatedterms such as hydrophilic, hydrophobic, humidity, etc. may be used.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A lithographic apparatus, comprising: a substrate table constructedto hold a substrate; a liquid supply system configured to provide aliquid to a space between an object on the substrate table and aprojection system; and a drain in the substrate-table configured tocontain liquid which leaks, in use, between an edge of the object andthe substrate table, wherein, in use, pressure of gas in the drain ismaintained to be substantially equal to ambient pressure of gas abovethe substrate table.
 2. The apparatus of claim 1, wherein, in use, thedrain is constructed and arranged never to be full of liquid.
 3. Theapparatus of claim 1, further comprising a liquid removal device in thedrain configured to remove liquid from the drain.
 4. The apparatus ofclaim 3, wherein the liquid removal device is a passive liquid removaldevice.
 5. The apparatus of claim 4, wherein the passive liquid removaldevice comprises a capillary channel.
 6. The apparatus of claim 1,wherein the drain comprises a chamber which is open to a top surface ofthe substrate table via a gap, the gap extending, in use, around theperiphery of the object.
 7. The apparatus of claim 6, further comprisinga divider positioned in the drain beneath the gap to split an opening ofthe gap into the drain into at least two.
 8. The apparatus of claim 7,wherein the divider comprises a mesh.
 9. The apparatus of claim 7,wherein the divider comprises a plurality of substantially downwardlyextending fins.
 10. The apparatus of claim 6, wherein a direct verticalpath leads from outside of the substrate table, through the gap into thedrain.
 11. The apparatus of claim 10, wherein the drain and the gap havea height and the height of the drain and the gap is such that the bottomof the drain is at least 1 mm from a top surface of the substrate table.12. The apparatus of claim 11, wherein the drain is at least 1 mm widerthan the gap.
 13. The apparatus of claim 1, wherein, in use, liquidenters the drain through the gap and the liquid has a contact angle ofgreater than 90° with surfaces of faces of the gap which oppose eachother.
 14. The apparatus of claim 13, wherein the faces define thenarrowest portion of the gap.
 15. The apparatus of claim 13, wherein thefaces are convex such that the gap narrows in a middle portion.
 16. Theapparatus of claim 13, wherein one of the faces is a surface of theobject.
 17. The apparatus of claim 16, wherein the other face is concaveand wherein the gap is narrowest at the entrance to the drain.
 18. Theapparatus of claim 1, wherein, in use, there is substantially no flow ofgas into the drain through the gap.
 19. A lithographic apparatus,comprising: a substrate table constructed to hold a substrate; a liquidsupply system configured to provide a liquid to a space between anobject on the substrate table and a projection system; and a chamber inthe substrate table in fluid communication with a gap surrounding, inuse, an outer edge of the object such that the chamber is open to anouter surface of the substrate table at a position around the outer edgeof the object, wherein, in use, the liquid has a contact angle ofgreater than 45° with surfaces which define the gap and face each otheracross the gap.
 20. The apparatus of claim 19, wherein, in use, theliquid has a contact angle of greater than 70° with the surfaces whichdefine the gap and face each other across the gap.
 21. The apparatus ofclaim 21, wherein the surfaces are convex such that the gap has anarrowing in a central portion.
 22. The apparatus of claim 19, whereinthe chamber has a width at least 1 mm wider than that of the gap. 23.The apparatus of claim 19, wherein the chamber has a height at leasttwice that of the gap.
 24. A lithographic apparatus, comprising: asubstrate table constructed to hold a substrate; a liquid supply systemconfigured to provide a liquid to a space between an object on thesubstrate table and a projection system; and a chamber in the substratetable in fluid communication with a gap surrounding, in use, an outeredge of the object such that the chamber is open to an outer surface ofthe substrate table at a position around the outer edge of the object,wherein, in use, the angle between surfaces defining the gap andsurfaces of the chamber onto which the gap open is at least 90°.
 25. Theapparatus of claim 24, wherein the angle is at least 100°.
 26. Alithographic apparatus, comprising: a substrate table constructed tohold a substrate, the substrate table comprising a passage which leadsto a chamber, the passage connecting the chamber to an outer surface ofthe substrate table and, in use, surrounds an outer edge of an object onthe substrate table; and a flexible flap extendable across the passageand biased substantially to block flow of gas between the passage andthe chamber and deformable by hydrostatic and/or hydrodynamic pressurefrom above to unblock the gap to allow passage of liquid from thepassage into the chamber.
 27. The apparatus of claim 26, wherein theflexible flap extends across two parts of the substrate table.
 28. Theapparatus of claim 26, further comprising a low pressure outletconfigured to remove liquid from the chamber.
 29. The apparatus of claim26, wherein the flexible flap comprises a perimeter of material flexibleenough so that local regions along its length are deformable to allowlocal passage of liquid from the passage into the chamber.
 30. Alithographic apparatus, comprising: a liquid supply system configured toprovide a liquid to a space between a projection system and a substrate;a first substrate table configured to hold a substrate, the firstsubstrate table having an edge with a face with a vertical component;and a second substrate table configured to hold a substrate, the secondsubstrate table having an edge with a face with a vertical component,wherein, in use, the liquid has a contact angle of greater than 45° withat least a portion of at least one of the faces.
 31. The apparatus ofclaim 30, wherein each face is part of a projection and forms an outermost boundary of the respective substrate table.
 32. A devicemanufacturing method comprising projecting a patterned beam of radiationthrough a liquid onto a substrate and collecting liquid which leaksbetween an edge of an object and a substrate table configured to holdthe substrate in a drain which is maintained at ambient pressure.
 33. Adevice manufacturing method comprising projecting a patterned beam ofradiation through a liquid onto a substrate and collecting liquid in achamber via a gap between an object and a substrate table configured tohold the substrate, the liquid having a contact angle of greater than45° with surfaces which define the gap and face each other across thegap.
 34. A device manufacturing method comprising projecting a patternedbeam of radiation through a liquid onto a substrate wherein liquid whichleaks between an object on a substrate table configured to hold thesubstrate, travels along a passage and moves a flexible flap extendingacross an outlet of the passage to expose the liquid to a low pressuresuch that it is removed from the flexible flap to allow the flexibleflap to re-block the passage.
 35. A device manufacturing methodcomprising projecting a patterned beam of radiation with a projectionsystem through a liquid onto a substrate which is supported by a firstsubstrate table, positioning a second substrate table next to the firstsubstrate table and moving both substrate tables together under theprojection system such that the second substrate table is moved underthe projection system, wherein edges of the first and second substratetables which are positioned next to each other during the moving eachcomprise a face with a vertical component, wherein the liquid has acontact angle of greater than 45° with at least a portion of at leastone of the faces.